In orthodontic care, a small amount of directed force is applied to malaligned teeth over a period of time, slowly moving the teeth into proper alignment. This force can be supplied by springs external to the mouth, that is, extraorally.
In U.S. Pat. No. 4,416,625, which issued Nov. 22, 1983, Armstrong utilizes an extension spring to supply extraoral force. Armstrong provides multiple spring end supports which can be used to stretch the spring to varying degrees, depending upon the amount of extraoral force needed.
In a subsequent patent, U.S. Pat. No. 4,553,934, which issued Nov. 19, 1985, Armstrong and Houser disclose means utilizing a compression spring to supply the extraoral force. A strap, which, when worn, ultimately applies force to a user's teeth, is attached to a rod passing through this spring. Distal ends thereof are attached to the rod and abut a sleeve, respectively; the position of the sleeve, which is adjustably mounted, determines the degree of compression applied to the spring, varying the extraoral force. The compression load on the spring can also be changed by adjusting the strap.
To be effective, an orthodontic device must be worn over an extended period of time each day. Further, orthodontists, in many cases, guarantee that they will be able to align a patient's teeth. For both purposes, it is desirable to record how long a patient actually wears an orthodontic device and the extraoral force exerted. Unfortunately, an orthodontic device that has means for measuring the force applied as a function of time is not available in the prior art.